Polarons, bipolarons, and π-dimers of bis(3,4-ethylene-dioxythiophene)-(4,4′-dialkyl-2,2′-bithiazole)-co-oligomers.: Direct measure of the intermolecular exciton transfer interaction

The oxidative behavior of bithiazole-ethylenedioxythiophene co-oligomers is described. The acceptor-donor-acceptor (A-D-A) compounds, 5,5'-bis(4,4'-dialkyl-2,2'-bithiazol-5-yl)-(3,4,3',4'-bis(ethylenedioxy)-2,2'-dithienyl) (1, 2), are sequentially oxidized by NOBF4 through the paramagnetic monocation to the diamagnetic dication. The monocations form diamagnetic pi-dimers, the allowed pi-pi electronic transitions of which are interpreted in terms of molecular exciton theory to give nearest-neighbor exciton coupling constants, J congruent to 0.2 eV. The spectra of the dications show that they are bipolarons; that is, the two charges share a common lattice deformation. The D-A-D co-oligomers, 5,5'-bis(3,4-ethylenedioxythien-2-yl)-4,4'-dibutyl-2,2'-bithiazole (3) and 5,5'-bis(3,4,3',4'-bis(ethylenedioxy)-2,2'-dithien-5-yl)-4,4'-dibutyl-2,2'-bithiazole (4), are oxidized in a single step to the corresponding bipolarons.